The use of radiation-sensitive functionality to induce crosslinking of a polymeric material is an advancing art, especially in the photographic industry where photographic films are composed of polymers having light sensitivity. However, it is also desirable to incorporate EB- or UV-crosslinkable functionality into elastomeric polymers. Elastomers containing such functionality could be utilized in pressure-sensitive adhesives (PSA's) and coatings to impart radiation curability, adhesive strength, and enhanced resistance to temperature, abrasion, solvents and ozone.
Applications employing external crosslinking reagents have certain inherent difficulties: such compositions require processing of the polymer with photoinitiators or crosslinking agents to facilitate the curing process. The toxicity and volatility of these compounds can present manufacturing difficulties and hazards. PSA's and coatings can have highly reactive unsaturation sites in the polymeric backbone to facilitate external free-radical crosslinking, but depending on the polymer, the unsaturation also provides sites at which the backbone can be degraded by reactions involving radicals.
U.S. Pat. No. 4,556,464 to St. Clair discloses a radiation curable adhesive composition suitable for use as a PSA, comprising a block polymer ABA formulation, where block A is polystyrene/isoprene or polystyrene/butadiene copolymer and block B is polyisoprene, a tackifier compatible with block B and a crosslinking agent compatible with block A.
It is desirable to have PSA's and coatings which are curable without the use of these additive compounds and have saturated polymeric backbones which are not degraded in reactions involving radicals. Therefore, radiation-reactive crosslinking agents may alternatively be incorporated into the polymer backbone, for instance, by copolymerizing with a radiation-sensitive vinyl polymerizable comonomer. Preparing such comonomers on a large scale is generally difficult. Radiation-reactive functionality may also be grafted onto the polymer backbone in a post-polymerization step, however, the resulting polymer is typically a heterogeneous product of low yield due to the difficulty of achieving adequate molecular contact at desired reaction sites. A good discussion of the mechanisms of photochemical reactions in polymers and examples of photoinitiators may be found in J. F. Radek, "Mechanisms of Photophysical Processes and Photochemical Reactions in Polymers Theory and Applications," Chapters 11 and 12, J. Wiley & Sons, 1987, which is hereby incorporated herein by reference.
European patent application 17,364 discloses copolymers curable by actinic radiation, such as UV light, made by incorporating from 0.1 to 10 percent by weight of the copolymer of an allyl benzoylbenzoate comonomer with a polymerizable monoethylenically unsaturated comonomer. These polymers are said to be useful in coating and impregnating formulations, and in adhesive, caulk and sealant formulations.
U.S. Pat. No. 4,315,998 to Neckers et al. discloses polymeric materials which incorporate photosensitive functionality via a nucleophilic substitution reaction. The polymeric materials serve as a platform for heterogeneous catalysts for a variety of photoinitiated chemical reactions.
U.S. Pat. Nos. 4,188,215 to Sato et al.; 3,923,703 to Fukutani et al.; 3,867,318 to Nishikubo et al.; 3,694,383 to Azami et al.; and 3,560,465 to Reynolds; and U.K. Patent 1,341,004 all relate to polymeric resins incorporating photosensitive functionality and/or processes for making such resins. These photosensitive resins are generally useful in photographic films.
Photosensitive coatings comprising a blend of a polymer and a photosensitive crosslinking agent are disclosed in U.S. Pat. No. 3,867,271 to Malatesta, et al. In this patent, a conjugated diene containing butyl rubber is cured by ultraviolet radiation with the aid of certain photosensitizers. A similar composition said to be useful as a coating for glass substrates is disclosed in U.S. Pat. No. 4,086,373 to Tobias et al., as comprising at least a rubbery thermoplastic organic polymer and an organic photosensitizer.
Photosensitive vinyl monomers are disclosed in U.S. Pat. Nos. 3,429,852 and 3,574,617 both to Skoultchi, wherein ethylenically unsaturated derivatives of substituted benzophenones are prepared by a method involving reacting a substituted benzophenone with an ethylenically unsaturated reagent such as glycidyl acrylate or glycidyl methacrylate. The resulting monomers may thereafter be homo- or copolymerized with a variety of conventional ethylenically unsaturated, i.e. vinyl, monomers. Photosensitive coating systems are prepared by depositing a solid polymer from an organic solvent or an emulsion onto a substrate. The photosensitive coating are said to be particularly suitable for use in various applications including, for example, lithography and chemical milling.
A similar concept is disclosed in U.S. Pat. No. 4,148,987 to Winey, wherein monoethylenically unsaturated derivatives of substituted benzophenones or acetophenones are prepared by a reaction of the benzophenone or acetophenone with a vinyl benzyl halide. These derivatives are polymerizable to form homopolymers, or copolymers with a wide variety of conventional ethylenically unsaturated monomers. The resulting polymers are sensitive to radiation, such as ultraviolet light having a wave length of 2,000 to 5,000 angstroms, and readily crosslink or cure upon exposure to such radiation. Adhesives, binders, coatings and impregnating compositions are made from the polymers.
Radiation-sensitive functionality have also been used to induce crosslinking of a polymeric material in the printing industries where printing plates are initially coated with polymers having light sensitivity. Such radiation-crosslinkable polymers have also been widely used as photoresists in the manufacture of semi-connectors or other engraved articles.
A process by which a polymer is functionalized with radiation-curable moieties is disclosed in U.S. Pat. No. 4,112,201 to Jones, wherein butadiene or isoprene copolymers having pendent unsaturated tetra-aliphatic quaternary nitrogen moieties, such as those derived from acrylic esters and acrylamides are useful as water soluble or inherently water-dispersable curable coatings. Such coatings are useful as protective and/or decorative coatings, paper coatings, textile fiber coatings, printing plates, photocurable imagable materials in photoresists, lithographic plates, etc. The coatings are said to be curable with light, with high energy radiation and with heat in the presence of free-radical catalysts to form insoluble crosslink coatings. The polymers are prepared by amination and a post-polymerization reaction. Likewise, the chemical modification of poly(vinylbenzylchloride) with a photosensitive compound including p-hydroxybenzophenone, 2-hydroxyfluorenone, potassium carbazole, and the like is disclosed in Bailey, et al., Journal of Applied Polymer Science: Polymer Chemistry Edition, vol. 17, 777-782 (1979).
In Azuma et al., Journal of Applied Polymer Science: Polymer Chemistry Ed., vol. 18, 781-797 (1980), the properties and preparation of cis-1,4-polybutadiene and polypentenamer having pendant functional groups including cinnamoyl groups are disclosed. Cinnamoyl groups are introduced into the polypentenamer, for example, by reacting a polypentenamer having hydroxymethyl groups with cinnamoyl chloride. Relationships involving the photosensitivity of cinnamoylated polypentenamer are discussed.
In Azuma et al., Journal of Applied Polymer Science, vol. 25, pp. 1273-1286 (1980), there is described an addition reaction of an .alpha.,.beta.-unsaturated carboxylic acid, such as cinnamic acid, to a polydiene, such as cis-1,4-polybutadiene, 1,2-polybutadiene and polypentenamer, in the presence of an acid catalyst. The unsaturated polydienes undergo cyclization in competition with the incorporation of carboxylate groups. Polymer morphology was said to indicate block segments alternating between cyclic segments and incorporated segments. The polymers were reported to have two glass transition temperatures, and the degree of incorporation against cyclization thereof to be controllable by reaction conditions.
In Azuma et al., Journal of Applied Polymer Science, vol. 27, pp. 2065-2078 (1982), there is disclosed a study conducted on the relation of photosensitive cyclized polydienes such as cis-1,4-polybutadiene, and polypentenamer having pendent cinnamate groups to the polymer structure. Photodimerization of cinnamate groups was said to be greatly affected by the mobility of the groups, while as the degree of cyclization increased, photosensitivity decreased.
From Azuma et al., Journal of Applied Polymer Science, vol. 28, pp. 543-557 (1983), it is known to react polyisoprene in o-dichlorobenzene solution with maleic anhydride to form polyisoprene modified with .alpha.-substituted succinic anhydride groups, and to further modify the polyisoprene by reaction with hydroxyethyl cinnamate in pyridine to incorporate cinnamate groups. It was stated that up to 75 mole percent of the repeating groups could be easily incorporated. Photosensitivity of the modified polyisoprene was said to be greater than that of cinnamate modified polypentenamer due to interaction of the free carboxylate groups. The interaction reduced the dependence of photosensitivity on mobility of polymer segments.
The preparation and use of copolymers of styrene and isobutylene is known in the art. Thus, such copolymers ranging from tough, glassy high polystyrene content copolymers for use in plastic blends, to rubbery low styrene content copolymers for use as impact modifiers, etc., have become well known in this art. Styrene and isobutylene have been copolymerized rather readily in the past under cationic polymerization conditions to yield these copolymers covering the entire compositional range. It is also known that blocky or random homogeneous copolymers can be produced by altering the copolymerization conditions, such as shown in U.S. Pat. No. 3,948,868 to Powers. This patent thus describes the production of random homogeneous polymers comprising at least two cationically polymerizable monomers such as isobutylene and styrene. This disclosure also includes a lengthy list of various olefinic compounds including isobutylene, styrene, .alpha.-methylstyrene and other such compounds. Furthermore, these compounds have been used in a variety of applications, including use as adhesives in connection with other materials taking advantage of the surface characteristics of the polyisobutylene sequences, as coatings, as asphalt blends, and in various plastic blends. As is discussed in the '868 patent, it is also well known to produce terpolymers including isoprene, but doing so reduces the overall polymer molecular weight rendering the production of high molecular weight polymers therefrom difficult, and complicating the overall production sequence.
There have also been attempts to produce various functionalized polymers. For example, U.S. Pat. No. 3,145,187 to Hankey et al. discloses polymer blends which include a vinyl chloride polymer, a surfactant, and a chlorinated olefin polymer, and the latter is said to include copolymers of various materials which can include isobutylene and styrene, as well as ring-alkyl styrenes, among a large number of other compounds, which olefin polymers can then be chlorinated by known methods.
The literature has also disclosed other routes for obtaining copolymers of isobutylene and styrene, such as that shown in U.S. Pat. No. 4,074,034 to Powers et al. which discloses the copolymerization of isobutylene with halomethylstyrene. This technique requires the use of vinylbenzyl chloride and the like as starting material, and utilizes a specified continuous solution process with solvent or mixed solvent systems in which the monomers are soluble under specified conditions. Aside from the need to employ the expensive vinylbenzyl chloride starting material, these processes also have limitations in terms of the quantity of aromatic chloromethyl functionality which can be incorporated in this manner without encountering excessive chain branching and gel formation during polymerization, and in terms of polymer recovery because of the reactivity of the benzylic chlorine under cationic polymerization conditions. See, "Isobutylene Copolymers of Vinylbenzyl Chloride and Isopropenylbenzyl Chloride," Journal of Applied Polymer Science, vol. V, Issue No. 16, pp. 452-459 (1969) in which the aromatic monomer is said to be a mixture of the para and meta isomers.
There has also been some interest in the halomethylation of isobutylene/styrene copolymers, such as discussed in a paper by Sadykhov et al. entitled "Chloromethylation of an Isobutylenestyrene Copolymer and Some of Its Chemical Reactions," Acerb. Neft. Khoz., 1979 (6) 34-9.
In an article by Harris et al. entitled "Block and Graft Copolymers of Pivalolactone . . . ," Macromolecules, 1986, vol. 19, pp. 2903-2908, the authors discuss the copolymerization of isobutylene with styrene and preferably a ring-methylated styrene. This article specifically discloses copolymerization with vinyl toluene, comprising a mixture of meta- and para-methylstyrene in approximately 65/35 amounts, and with para-methylstyrene, for the purpose of producing thermoplastic elastomer pivalolactone copolymer systems with no auto-oxidizable aliphatic unsaturation. The article fails to recognize any difference between the use of vinyl toluene and para-methylstyrene, and in any event, even when it employs the latter, it employs conditions which result in copolymers having the properties, including heterogeneous compositional distribution and very broad molecular weight distribution for the unfractionated copolymer, as set forth in Tables 4 and 5, which include an M.sub.n for the unfractionated copolymer of 16,000, M.sub.w /M.sub.n of 17.45, and a 4-methylstyrene content in the polymer which varies considerably from the monomer feed and varies significantly as a function of molecular weight.
Finally, there are also articles which discuss copolymers of isobutylene and para-methylstyrene without discussing any method for preparing them. These articles include Sadykhov, et al., "Studies of Oxidative Thermal Degradation of Copolymers of Isobutylene with m- and p-Methylstyrenes in a Solution of Mineral Oils," Uch. Zap. Azerb. Un. t. Ser. Khum., 1975 (304), 87-92, and other such articles. Furthermore, in Toman, et al., "Isobutylene Polymers and Copolymers with Controlled Structure", App. 78/7, 339, (Nov. 10, 1978), there is reference to the copolymerization of isobutylene with vinyl aromatic monomers. The search has thus continued for useful molecular weight copolymers of isobutylene and alkyl styrenes, and in particular for functionalized copolymers of this type which can be cross-linked, and otherwise used in a variety of applications.
Polymers with a saturated hydrocarbon backbone are well known to possess good environmental and aging resistance which makes them highly desirable in a variety of applications. Furthermore, rubbery copolymers containing major amounts of polyisobutylene are well known to possess low permeability, unique damping properties, and low surface energy which makes them particularly highly desired in many applications. However, the "inertness" of these saturated hydrocarbon polymers, their low reactivity and incompatibility with most other materials, and the difficulties in adhering them to, or using them in conjunction with most other materials has restricted their use in many areas.
In commonly assigned U.S. Ser. No. 441,575, filed Nov. 22, 1989, which is also a continuation-in-part of co-pending U.S. Ser. No. 416,503 filed Oct. 3, 1989, which is a continuation-in-part of co-pending U.S. Ser. No. 199,665 filed May 27, 1988; and co-pending U.S. Ser. No. 416,713 filed Oct. 3, 1989, which is a continuation-in-part of U.S. Ser. No. 199,665 filed May 27, 1988, the disclosures of which are hereby incorporated by reference, it was theorized that the introduction of controlled amounts of the desired specific functionality as pendant groups on the saturated hydrocarbon backbone would greatly extend usefulness by permitting these polymers to be adhered to other surfaces and/or to be co-reacted with or compatibilized with other functional polymers by "grafting" or crosslinking reactions. It was further theorized that the introduction of pendant functionality of the right type and amounts would permit these saturated hydrocarbon polymers to be "painted" or coated with or on other materials, and/or to be laminated with or dispersed in other materials to yield composite materials with a desired combination of properties.
As has been already pointed out, the fact that benzylic halogen functionality constitutes a very active electrophile that can be converted to many other functionalities via S.sub.N 2 nucleophilic substitution reactions has long been recognized, and the chemical literature is replete with examples of these reactions. Selective conversions in high yield to many functionalities, including the following have been reported: aldehyde, carboxy, amide, ether, ester, thioester, thioether, alkoxy, cyanomethyl, hydroxymethyl, thiomethyl, aminomethyl, cationic ionomers (quaternary ammonium or phosphonium, S-isothiouronium, or sulfonium salts), anionic ionomers (sulfonate and carboxylate salts), etc. In addition, the literature described many examples in which a benzylic halogen is replaced by a cluster of other functionalities by nucleophilic substitution with a multifunctional nucleophile such as: triethanolamine, ethylene polyamines, malonates, etc.
Nearly all of this previous work has been with simple, small (i.e. non-polymeric) molecules containing the aromatic halomethyl (or benzylic) functionality. However, a considerable amount of art also exists on nucleophilic substitution reactions involving chloromethyl styrene and polystyrenes containing aromatic chloromethyl groups to introduce other functionalities. Much of this work involves reactions with "styragels" or lightly crosslinked polystyrenes containing various amounts of benzylic chlorine. While many of the same nucleophilic substitution reactions previously reported for small molecules containing benzylic chlorine have been achieved in "styragels," it has been necessary to modify reaction conditions, and in particular to often employ phase transfer catalysts, in order to promote the desired substitution reaction. Reactions involving the benzylic chlorine in polystyrene have been more difficult to achieve than in simple small molecules because of the greater difficulty in achieving the intimate contact required between the reactants when one of the reactants (the aromatic chloromethyl moiety) is in a separate polymeric phase from the other reactant. Yields have also generally been lower and side reactions are more prevalent in the reactions involving the benzylic chlorine in polystyrene. However, since most of the work has been with "styragels," it has generally not been necessary to achieve high conversion in "clean," highly selective substitution reactions in order to preserve polymer solubility. Good recent review of this work involving chloromethyl styrene and "styragels" containing benzylic chlorines are in the literature. See Marcel Camps et al., in "Chloromethylstyrene: Synthesis, Polymerization, Transformation, Applications" in Rev. Marcromol. Chem. Physics, C22(3), pp. 343-407 (1982-83); JMJ Frechet in Chemical Modification of Polymers via Phase Transfer Catalysts in Crown Ethers and Phase Transfer Catalysts in Polymer Science, edited by Matthews and Canecher and Published by Plenum Press, NY, 1984; and Jean-Pierre Montheard et al., in "Chemical Transformations of Chloromethylated Polystyrene" in JMS-Rev. Macromol. Chem. Phys., C-28 (3 & 4), pp. 503-592 (1988).
Previous workers have not applied nucleophilic substitution reactions to isobutylene/para-methylstyrene/para-bromomethylstyrene terpolymers to produce versatile, substantially saturated, pendant functionalized, soluble copolymers.